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Old 16th June 2004, 09:07 AM   #11
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Hi,

Yes the circuit is still in the works. I have however had difficulties getting a layout and concept done that satisfies my need for simple adjustment using resistor ladders.

This has made me think along a different approach. I am wondering if a fully potentiometer controlled device would satisfy my needs. Choosing this approach would mean that the user would need to “reverse engineer” the settings by measuring the values of the potentiometers and inserting these values into some equations to determine Q and fc.

This is a rather clumsy way of adjustment control – comparing to the mox boards – but I have been unable to find a better way until now. Ideas are most welcome.

I have a working circuit – in the simulator - with potentiometers, but it needs to be tested I real life, and I don’t have the time right now.

Please comment on the circuit posted by netgeek here

http://www.ethanwiner.com/spectrum.html figure 3

\Jens
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Old 17th June 2004, 03:53 AM   #12
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HI,

I have been attempting a similar project with little luck. I want a 3-band parametric EQ, and want adjustable Q, gain, and freq. The problem lies in the fact that I want to adjust all of these parameter via digital potentiometer. It is very difficult for *me* to find the solution to this problem, while retaining signal quality.

We need more than 6dB roll-off for sure, which necessitates a 2-pole filter, only complicating my quest for adjustability. I am aiming for a 3-pole with 18dB roll-off, while retaining the adjustable parameters. I have looked into the state-variable concept, which provides the adjustable Q and gain that I am seeking...along with the center frequency. Those are all easily adjustable, but the problem lies in the flat 6dB roll-off curve.

In order to have a sharper drop and less adjacent band interactance, I would have to add filters which greatly increases the difficulty of controlling the units based on resistance values only.

Perhaps one of you guys has created a "digital capacitor?"

How are you managing parameter control?





-Matt
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Old 31st August 2004, 11:47 PM   #13
DcibeL is offline DcibeL  Canada
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I am interested to know how your project is going Jens. I am going to be designing and building a parametric equalizer for my thesis project in school, and am interested to know how other people have designed such a device so that I have some reference if I get lost while designing mine. Thank-you for that excellent link to the Ethan Winer website, I think that information will come in very handy. Is your equalizer very similar to the schematic on that website? For example, are you using the same TL074 op-amps?

As it is only the beginning of the school year, I am just getting started on this project, and am just done some preliminary research so far.
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Old 1st September 2004, 04:50 AM   #14
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Hello,

I have not had time to do much work on this. The project is however still active and the design is in the works.

First tests using a circuit similar to that of Ethans are successful, put the adjustment are rather clumsy and until I’m satisfied I will not publish the result.

DcibeL if you find any smart ways of making resistor ladders work simply in your project, please let us know.

\Jens
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Old 12th September 2004, 05:52 AM   #15
DcibeL is offline DcibeL  Canada
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I have now had the opportunity to discuss my project with my advisor, and he would like to see my parametric equalizer be built using a programmable IC, which will be controlled by a PIC microcontroller preferrably using I2C protocol, and of cource have a nice LCD display. My task now is to try see if such an IC exists and if not, then I will have to modify my project to make it more interesting.
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Old 13th September 2004, 03:11 PM   #16
tiroth is offline tiroth  United States
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Yes, you are lucky. TAS3103. I hope you can use TSSOP. The TAS3103EVM would be a good thought for a project.
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Old 13th September 2004, 09:58 PM   #17
DcibeL is offline DcibeL  Canada
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Thank-you very much for informing me of that IC. I had looked the other day and found a few chips, but none of them did exactly what I wanted them to. I am not familiar with the TSSOP package so I will have to check (1) If the pins are spaced large enough that they can be soldered by hand and (2) If our PCB machine can make tracks for surface mount devices. I am almost certain that I won't be able to use this IC, but I will investigate.

I had a visit with my project advisor today, and we are almost set on a design for this thing. As of right now, we are back to a complete op-amp controlled circuit, using a PIC and digital pots to control it. This way, it can have an LCD displaying the values, and buttons that don't wear out to control it, rather then analog pots that do wear out. I am actually quite exited about this design, hopefully I can make it work.
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